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The rational addiction (RA) model of Becker and Murphy (Becker GS, Murphy KM. A theory of rational addiction. J Pol Econ 1988; 96(4): 675-700) has rapidly become one of the standard models in the literature on addictive behaviour. This paper reviews some theoretical issues surrounding its use, and indicates areas in which caution should be used in applying this model.
The forelimbs of 12 genera of New World monkeys, two genera of Old World monkeys, and a gibbon were dissected. Of the 54 muscles examined, 19 exhibited significant intergeneric variation. We present arguments for which morphologies are primitive and which are derived within platyrrhines and within anthropoids. We conclude that the forelimbs of Cebus apella and Callicebus moloch represent good models of the ancestral anthropoid morphology. Thus among living anthropoids they are most appropriate for comparisons with early fossil anthropoids. They are also useful for determining whether myological anomalies of human aneuploids are atavistic. Wagner tree analyses were conducted to assess the value of these myological characters in phylogenetic studies of platyrrhines. In most respects the Wagner trees were consonant with phylogenies previously proposed, although some hypothesized trees are less parsimonious than others in explaining our data. There is an unexpected number of derived features shared by Aotus and the Atelines. There are marked dissimilarities in forelimb musculature between Aotus and Callicebus.
Analyses were performed on lipid data from the NHLBI Veteran Twin Study. The analyses focused on longitudinal multivariate models, describing how the genetic effects on lipids vary over time. Our pedigree-based model selection approach allows simultaneous estimation of both covariance structure parameters and regression parameters. The analyses reveal strong correlations between additive genetic effects over time, implying that genetic effects on lipids are somewhat constant throughout the life span represented within this sample. Both univariate preliminary analyses and robust fitting applied to the longitudinal models indicate that several assumptions underlying the twin analyses are violated. Although variance component and correlation parameter estimates are not much changed by robust fitting analyses, questions remain about the behavior of parameter estimates in multivariate genetic models under departures from model assumptions.
Noise limitation on the detected spatial resolution, described by the Rose Model, is well known in X-ray imaging and routinely used in designing X-ray imaging protocols. The purpose of this article is to revisit the Rose Model in the context of MRI where image data are acquired in the spatial frequency domain. A k-space signal-to-noise ratio (kSNR) is introduced to measure the relative signal and noise powers in a circular annulus in k-space. It is found that the kSNR diminishes rapidly with k-space radius. The Rose criterion that the voxel SNR approximately 4 is translated to kSNR cutoff values was tested using theoretical derivation and experimental histogram analysis. Experiments demonstrate that data acquisition beyond this cutoff k-space radius adds little or no information to the image. In order to reduce the noise limit on spatial resolution, the signal strength must be improved through means such as increasing the coil sensitivity, contrast enhancement, and signal averaging. This finding implies that the optimal k-space volume to be sampled or the optimal scan time in MRI should be matched to the relative SNR level.
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The increased appreciation of the effects socio-ecological factors have on health, witnessed over the last few decades, has given rise to many international, national, and local Health For All (HFA) initiatives tasked with addressing them. However, such initiatives have had to operate within environments which were not specifically designed for them or for the new social (rather than medical) perspective on health they were based upon. As a result, they have been facing significant barriers and constraints to fulfilling their mission. This paper explores the constraints which are imposed on such initiatives by the various environments within which they are nested. Drawing upon our experience in evaluating European Healthy City (HC) projects and English Health Action Zones (HAZs), we develop a dynamic conceptual model which shows how the national, governmental policy, interorganisational, organisational, and initiative environments relate with each other and their cumulative effects on initiatives. We argue that this model, and the principles on which it is based, can be used constructively to identify constraints facing HFA-type initiatives in many countries. We use our case study of English HCs and HAZs to illustrate the applicability of the model in a particular national context. We, first, interpret the model to reflect differences and similarities between their respective environments and trace the sources of the different constraints they encountered. We, then, show how an alternative structural configuration could enable some of these constraints to be eliminated. We argue that what is needed for HFA initiatives to be able to fulfill their brief in full is for governments to rethink existing organisational structures and update them to match the evolution of ideas on health which have emerged over the last decades.
Assembling pieces of the standard model of the immune system, a saver system subset is proposed, comprising a continuously active circulating subsystem of saver cells and saver bodies which inspect every cell and antigen and saves/interrupts from self attack.
The rheological and functional properties of food components are related to their molecular structure, morphology, and atomic mobilities. NMR provides a powerful tool for elucidating chemical structures, molecular conformations, and interactions of components in food systems. Quantitative analysis of sugars, fats, and other principal compounds in complex food systems was achieved by high-resolution liquid NMR. In addition to information available from liquid experiments, solids NMR experiments can reveal differences and changes in crystal packing of structures in food model systems. Interpretation of experimental results is enhanced by molecular modeling of key food compounds. Models for fat crystallization are carried out to enhance understanding of the molecular structures involved in the fat crystallization process. Recently, MRI has also shown significant impact on food science and technology. Some examples of NMR applications are given in this presentation.
A set of 538 inhibitors of the tyrosine kinase, Syk, including purines, pyrimidines, indoles, imidazoles, pyrazoles, and quinazolines, has been analyzed using a stepwise nonparametric regression (SNPR) algorithm, which has been developed for QSAR studies of pharmacological data. The algorithm couples stepwise descriptor selection with flexible, nonparametric, kernel regression, to generate structure-activity relationships. A further 371 molecules have been used as a test set to evaluate the models generated. Descriptors were selected using an internal monitoring set, and models were assessed using 10% of the principal (538-compound) data set, selected randomly, as an external validation set. The best model had a Q(2) of 0.46 for the external validation set. Test set predictions were significantly less accurate, partly due to the higher mean activity of the test molecules. However at a more coarse-grain level the SNPR models classified active molecules accurately, giving good enrichments. The data sets are difficult to model accurately and SNPR performs better than multilinear regression and a neural network analysis. In the additive implementation of SNPR multidimensional models are considered as a sum of single dimensional regressions. This makes the resultant models easily interpretable. For example, in the most predictive SNPR models, there is a clear nonlinear relationship between hydrophobicity (AlogP98) and inhibitory activity.
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The method of paired comparisons belongs to a small group of techniques that provide explicit information about the consistency of individual and aggregated choices. This article investigates the link between the individual- and group-level judgments by extending R. D. Luce's (1959) model, which was originally developed for individual choice behavior, to a mixed-effects paired comparison model. It is shown that standard multilevel software for binary data can be used to estimate the model. The interpretation of the paired comparison parameters and statistical model tests are discussed in detail. An extensive analysis of an experimental study illustrates the usefulness of a hierarchical approach in modeling multiple pairwise judgments.
Dielectric relaxation measurements of a typical small molecular glassformer, dipropyleneglycol dibenzoate show the presence of two secondary relaxations. Their dynamic properties differ in the equilibrium liquid and glassy states, as well as the changes during structural recovery after rapid quenching the liquid to form a glass. These differences enable us to identify the slower secondary relaxation as the genuine Johari-Goldstein (JG) beta-relaxation, acting as the precursor of the primary alpha-relaxation. Agreement between the JG beta-relaxation time and the independent relaxation time of the coupling model leads to predicted quantitative relations between the JG beta-relaxation and the alpha-relaxation that are supported by the experimental data.
We develop a model for somatic growth in fishes that explicitly allows for the energy demand imposed by reproduction. We show that the von Bertalanffy (VB) equation provides a good description of somatic growth after maturity, but not before. We show that the parameters of the VB equation are simple functions of age at maturity and reproductive investment. We use this model to show how the energy demands for both growth and reproduction trade off to determine optimal life-history traits. Assuming that both age at maturity and reproductive investment adapt to variations in adult mortality to maximize lifetime offspring production, our model predicts that: (i) the optimal age of maturity is inversely related to adult mortality rate; (ii) the optimal reproductive effort is approximately equal to adult mortality rate. These predictions are consistent with observed variations in the life-history traits of a large sample of iteroparous freshwater fishes.
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In a previous publication, it was demonstrated that the abdominal subcutaneous fat layer thickness (SFL) is strongly correlated with the abdominal electrical impedance when measured with a transversal tetrapolar electrode arrangement. This article addresses the following questions: 1) To which extent do different abdominal compartments contribute to the impedance? 2) How does the hydration state of tissues affect the data? 3) Can hydration and fat content be assessed independently? For simulating the measured data a hierarchical electrical model was built. The abdomen was subdivided into three compartments (subcutaneous fat, muscle, mesentery). The true anatomical structure of the compartment boundaries was modeled using finite-element modeling (FEM). Each compartment is described by an electrical tissue model parameterized in physiological terms. Assuming the same percent change of the fat fraction in the mesentery and the SFL the model predicts a change of 1,24 omega/mm change of the SFL compared to 1,1 omega/mm measured. 42% of the change stem from the SFL, 56% from the mesentery and 2% from changes of fat within the muscle compartment. A 1% increase of the extracellular water in the muscle is not discernible from a 1% decrease of the SFL. The measured data reflect not only the SFL but also the visceral fat. The tetrapolar electrode arrangement allows the measurement of the abdominal fat content only if the hydration remains constant.
The dimensional structure of emotion was investigated using self reports of induced mood and idiographic and nomothetic analyses. Subjects attended four experimental sessions during which an array of affective states was induced via auditory, visual, and imaginal channels. For each of 118 stimulus events, subjects self-rated their response. Factor analysis yielded the predicted bipolar factors of valence and arousal: these were obtained in group-aggregated analysis and subsequently confirmed as change dimensions at the intraindividual level. Controversy over the fundamental dimensions of affective space was considered with respect to methodological issues such as factor rotation and sampling of data space. Valence and arousal are discussed as motivational, driving parameters of affective experience and a dynamical systems conceptualization of emotion is proposed.